Spinneret assembly for composite filaments



Nov. 10, 1970 I w W.

INVENTOR JOH/V 65,250 awn/v,

Nov. 10, 1970 J. G. ULLMAN 3,538,544

I SPINNERET ASSEMBLY FOR COMPOSITE FILAMENTS Filed May 9, 1968 2 Sheets-Sheet 2 mam/71v,

United States Patent 3,538,544 SPINNERET ASSEMBLY FOR COMPOSITE FlLAMENTS John Gerson Ullman, Martinsville, Va., assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware Filed May 9, 1968, Ser. No. 727,992 Int. Cl. D011! /28 US. Cl. 18-8 5 Claims ABSTRACT OF THE DISCLOSURE A spinneret assembly comprising sandwiched filter block, distribution plate and spinneret plate is designed to produce a plurality of uniform sheath-core filaments with accurate regulation of sheath thickness without overcrowding extrusion orifices. The flow channels and passages are shaped and interconnected to provide uniform pressure and distribution of the sheath and core polymers across the plurality of extrusion orifices.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to an apparatus for the production of bicomponent filaments and, more particularly, to an improved spinneret assembly for extrusion of sheathcore filaments.

Prior art Filaments consisting of two or more components are well known in the art and are generally produced by extruding the different components from the spinnerets in side-by-side relationship or in an accentrically disposed sheath-core arrangement. With the latter type of filament, it has been found difficult to prevent variations in the sheath thickness with the result that product uniformity was less than desirable. United States Pat. No. 3,244,785, discloses a process and apparatus which permits more accurate regulation of the sheath thickness and thus produces a more uniform product. While few problems are encountered with this arrangement when the number of filaments extruded from a given spinneret is small, the extrusion of larger numbers of filaments from a single spinneret inhibits equal distribution of the two polymers to the spinneret plate without undesirable crowding of the extrusion orifices.

SUMMARY OF THE INVENTION The deficiencies of the prior art spinneret assemblies are overcome by the instant invention which comprises sandwiched filter block, distribution plate and spinneret plate elements. The filter block has two separate filtration cavities on its upper face. The juncture of the filter block and the distribution plate define first. second and third upper fiow channels. The first and second upper flow channels are connected at their respective ends by connecting upper flow channels. The first upper channel and one of the filtration cavities are connected by a distribution passage. The third upper flow channel and the other of the filtration cavities are connected by a second distribution passage. The juncture of the distribution plate and the spinneret plate define a lower flow channel. The ends of the lower flow channel are connected to the third upper flow channel by sheath meter passages. The second upper flow channel is connected with the central portion of the lower flow channel by core meter passages, each of which terminates at the face of a cylindrical projection. This projection is in the central portion of the lower fiow channel and in close proximity to the upper surface of the spinneret plate. The spinneret plate has core spinneret pasice sages. coaxial with the core meter passages which connect the lower surface of the spinneret plate with the lower flow channel. The spinneret plate additionally has angular sheath spinneret passages which connect the lower flow channel with the core spinneret passages at a junction between the lower fiow channel and the lower surface of the spinneret plate.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of the spinneret assembly of the instant invention.

FIG. 2 is a view taken along line II-II of FIG. 1, illustrating the bottom surface of the filter block.

FIG. 3 is a view taken along the line IIIIII of FIG. 1, illustrating the bottom portion of the distribution plate.

FIG. 4 is a view taken along line IVIV of FIG. 1, illustrating the top surface of the spinneret plate.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, the spinneret assembly chosen for purposes of illustration includes a filter block 10 having separate filtration cavities 12, 14 from which different viscous polymeric materials are discharged through distribution passages 16, 18. Material from cavity 12 passes into third upper flow channel 20 and through holes or sheath meter passages 22 in distribution plate 21 into lower fiow channel 24 (see FIG. 3). The material then flows into central portion 24a of the lower flow channel from which it passes through holes 26 and 28, the core and sheath spinneret passages, in spinneret plate 38 to form the sheath of a bicomponent filament.

The core material is discharged from cavity 14 into first upper flow channel 30 and passes into second upper flow channel 30a from which it is discharged through core meter passages 32 into the central portion of core spinneret passages 26 of spinneret plate 38 to form the core of the bicomponent filament.

The spacing between cylindrical projections 34 and the top of spinneret plate 38 is adjusted in relation to the pressures on the polymers and the sizes of the How passages to control the relative amounts of sheath and core formed in holes 26. The width of projection 34 relative to the diameter of hole 26 is also an important design consideration in regulating the sheath-core distribution in hole 26. The rate of polymer flow through hole 28 will, of course, depend on the diameter and length of the passage, on the polymer viscosity and on the pressure in flow channel 24a.

At the juncture of passages 26 and 28, the polymers are combined in an essentially side-by-side relationship and extruded through spinning orifice 36. Formation of sheathcore filaments by first forming a concentric sheath-core column of the polymer in one flow passage and then combining this column with additional sheath material from a second flow passage is disclosed in United States Pat. 3,244,785. Additional details relative to this procedure may be found therein.

Wider spicing of the flow passages, especially passages 32 and correspondingly passages 26, allows cylindrical projections 34 to have a larger diameter. A projection 34 having a larger diameter creates a longer flow path for the sheath polymer and consequently induces a larger pressure drop across the face of a projection. The result is a smaller percentage variation in sheath thickness when spinning polymer pressure varies.

Flow channels 30a and 24a preferably tapered from either end toward the center of the assembly to compensate for temperature gradients in the polymer from the inside to the outside of the assembly as disclosed in United States Pat. 3,225,383.

The upper flow passages may be formed by recesses in the filter block as illustrated. However, alternatively and perhaps preferably, they can be formed by appropriate recesses in the top of the distribution plate 21. Similarly, the lower flow passage can be formed by appropriate recesses in spinneret plate 38 rather than in the distribution plate 21.

The spinneret assembly is, of course, provided with a suitable top plate, and the various elements are bolted or otherwise fastened together, for instance, as disclosed in the United States Pat. 3,262,153.

The apparatus of this invention has the advantage of providing a relatively simple arrangement for extruding a considerable number of sheath-core filaments without undue crowding of the spinneret orifices or enlargement of the spinneret assembly. Crowding is obviously undesirable, since it leads to difiiculties in proper cooling of the freshly extruded filaments. Enlargement of the assembly is expensive and otherwise undesirable due to space limitations.

What is claimed is:

1. A spinneret assembly for production of synthetic sheath-core filaments comprising sandwiched filter block, distribution plate and spinneret plate elements, said filter block having two separate filtration cavities on its upper face, the juncture of said filter block and said distribution plate defining first, second and third upper flow channels said first and second upper flow channels connected at their respective ends by connecting upper flow channels, said first upper flow channel and one of said filtration cavities connected by a distribution passage, said third upper flow channel and the other of said filtration cavities connected by a second distribution passage, the juncture of said distribution plate and said spinneret plate defining a lower flow channel, the ends of said lower flow channel connected to said third upper flow channel by sheath meter passages, said second upper fiow channel connected with the central portion of said lower flow channel by core meter passages each of which terminates at the face of a cylindrical projection which projection is in said central portion of said lower flow channel, the face of said cylindrical projection in close proximity to the upper surface of said spinneret plate, said spinneret plate having core spinneret passages coaxial with said core meter passages connecting the lower surface of said spinneret plate with said lower flow channel, said spinneret plate additionally having angular sheath spinneret passages connecting said lower flow channel with said core spinneret passages at a junction between said lower flow channel and said lower surface of said spinneret plate.

2. The spinneret assembly of claim 1 where in said lower flow channel is substantially U'shaped, said sheath meter passages connecting at the extremities of said lower flow channel.

3. The spinneret assembly of claim 1 wherein said second upper flow channel is wider than and has substantially the same length as said first upper flow channel.

4. The spinneret assembly of claim 1 wherein said second upper flow channel is tapered from a minimum depth at its outer portion Where connected by said connecting upper flow channels.

5. The spinneret assembly of claim 1 wherein said upper flow channels are defined by recesses in said filter block and said lower flow channel is defined by a recess in said distribution pIate.

References Cited UNITED STATES PATENTS 3,225,383 12/1965 Cobb 18-8 3,244,785 4/1966 Hollandsworth 264-171 3,262,153 7/1966 Mercer et a1 l88 3,350,741 11/1967 Yoshida et al l8-8 3,375,548 4/1968 Kido et al. 18-8 WILBUR L. McBAY, Primary Examiner 

